Portable motorized grips are already known for use for the above-mentioned purposes, the grips comprising a pair of jaws identical in mirror-image, pivoted, at intermediate points along their length, to a supporting structure and arranged symmetrically in relation to a plane running parallel with the longitudinal direction of the grip; located in the free end-sections, projecting outwardly and normally spread apart, of the jaws are seats adapted to receive and hold the curved opposing parts of "C" clips, each of which is transferred to its seat, while turning its open side towards the end-sections, by the action applied to the relevant back by a thrust-plate parallel with the jaws and controlled, by means of a rod integral therewith, in such a manner as to carry out alternate longitudinal movements; and the grip comprising a stop adapted to prevent withdrawal of the back of the clip inserted into the seat when the free end-sections of the jaws are brought together in order to clamp the clip.
In this known grip, the thrust-plate lies in the plane containing the jaws and the rod integral therewith constitutes the piston-rod of a double acting pneumatic jack. Insertion of the clip in the seats located in the free end-sections of the jaws is complete when the thrust-plate is in the terminal position towards the said seats; clamping of the clip is completed while the plate approaches its terminal position in the opposite direction. Finally, the stop which prevents withdrawal of the back of the clip which has been clamped is snap-acting and consists of a pawl adapted to locate itself, under the action of a spring, behind the central part of the back of the clip inserted into their seats.
The design of the known grip, described hereinbefore, has certain serious disadvantages which greatly affect its reliability and drastically limit the fields of application.
One of these disadvantages is that the snap-acting stop, consisting of a spring-loaded pawl, is totally incapable of withstanding thrusts, often of the order of some hundreds of kg, acting thereupon while the clips are being clamped. A stop of this kind is easily rendered unserviceable by breakage of the spring or seizure of the pawl, and if the grip is used, as naturally intended, for upholstering or the like, i.e. for clamping substantially less rigid clips, the clips may be deformed irregularly or are lost because they are expelled prematurely from their seats in the jaws.
Another no less serious disadvantage is that the jack which actuates known grips is of the pneumatic type. Since in areas where the grips in question are used, compressed air is not generally available in excess of 6 to 7 atm., it is obvious that a thrust of the magnitude mentioned hereinbefore can be obtained only at the cost of using jacks of a bulk and weight incompatible with the requirements of a portable unit.